Correct vehicle suspension and geometry improves the directional stability, tracking, cornering, and overall driveability of a vehicle while also increasing tire tread life and wear. Two primary vehicle wheel alignment characteristics are toe, which is generally defined as the slanting of the wheels toward the front or back of the vehicle, and camber, which is generally defined as the sloping of the wheels toward the top or bottom of the vehicle.
Different vehicle models are designed to be manufactured with different wheel geometries to optimize certain performance characteristics. Even versions of the same model may be manufactured with different wheel geometries, so as to optimize vehicle performance for the driving conditions typically encountered in a particular locality. So, an aligner should be able to measure the characteristics of vehicles having many different settings.
While several different measurement techniques are currently employed, the accurate measurement of wheel alignment is a surprisingly difficult problem to solve in a cost and time efficient manner. In a typical manufacturing process, the wheel alignment is measured in all vehicles as a part of the manufacturing process, and the wheel alignment of a relatively small percentage of vehicles, such as 4%, is measured a second time as an audit for determining the accuracy of the aligner used in the manufacturing process.
It would be desirable to audit a higher percentage of vehicles, so that the accuracy of the alignment process could be improved. However, the audit time of current alignment audit equipment is such that a significantly higher audit rate is not viable. Typical auditing devices currently in use are quite slow, and so cannot keep pace with a production line. So, for example, if one hundred cars are produced in a production line in a given period of time, only four cars may be able to be audited in that given period of time, to obtain a 4% audit percentage. While it may be possible to add more auditing devices to increase the audit percentage, the cost of so doing may be prohibitive.
In light of the above, it can be appreciated that an alignment system that is less expensive, quicker, and more accurate than known systems is a significant advance in the art. Manufacturers may be expected to save on warranty repairs, and vehicle owners may be relieved of the burden of purchasing a new vehicle that is not correctly aligned.
U.S. Pat. No. 5,150,515 of Merrill et al., owned commonly with the present invention, teaches a measurement system that combines a geometric wheel aligner with a dynamic wheel aligner, and so provides a useful reference of prior wheel alignment techniques. U.S. patent application Ser. No. 08/700,666 of Chapin et al. now U.S. Pat. No. 5,812,256, owned commonly with the present invention, teaches a vision system for wheel alignment using moving vision sensors. The moving sensors are described as translating vertically up and down and then side to side to "paint" a target.
Each of the documents referred to herein are hereby incorporated by reference to the extent they include information helpful to a proper understanding of the present invention. It should be understood that no documents or descriptions herein are admitted to be "prior art," but are only mentioned to place the invention in context and to assist in a proper understanding of the invention.